1. Field of the Invention
The invention relates to a telephone accessory, more particularly to a power switch device that utilizes phone loop signals to control the supply of electrical power to a telephony instrument.
2. Description of the Related Art
Most conventional telephony instruments, such as facsimile machines, telephone answering machines, and wireless telephone sets, are configured to draw electrical power continuously from a power source, and thus consume electrical power even when in an on-hook or waiting state. FIGS. 4 and 5 illustrate two conventional schemes for reducing electrical power consumption of a telephony instrument. In FIG. 4, the telephony instrument 703 is connected to a local phone loop via a pair of telephone wires (A, B), and is further connected to an AC power source (not shown) via a pair of power lines (C, D). A power switch 701 is connected to the telephone wires (A, B), and is further connected to the AC power source. The power switch 701 makes or breaks connection between the power source and the power line (C) in accordance with phone loop signals at the telephone wires (A, B). In FIG. 5, the telephony instrument 703 is connected to the local phone loop via a pair of telephone wires (A, B), and is further connected to a solar cell 704. A power switch 702 is connected to the telephone wires (A, B), and is further connected to an AC power source (not shown) via power lines (E, F). Similar to the circuit of FIG. 4, the power switch 702 makes or breaks connection between the telephony instrument 703 and the solar cell 704 in accordance with phone loop signals at the telephone wires (A, B). Because the telephony instrument 703 is normally disconnected from the AC power source or the solar cell 704 when in the on-hook or waiting state, electrical power consumption can be reduced. However, because the power switches 701, 702 require connection to the AC power source, the aforesaid schemes cannot be relied upon to ensure operation of the telephony instrument 703 in the event of power failure.
In order to ensure operability of telephony instruments in the event of power failure, it has been proposed heretofore to connect the aforesaid power switches 701, 702 to an uninterruptible power supply. However, use of the uninterruptible power supply results in added expense to consumers.